Gas turbine engines such as those used in industrial, marine, vehicle, and aerojet applications, may include multiple stages of compressors. In a typical arrangement air is first drawn over a first compressor stage that elevates the air pressure to a desired level. The air, while passing in a generally axial direction through the engine, then crosses successive compressor stages that further raise the air pressure.
It has been found that bleed valves can be used at various points on a gas turbine engine to assist in maintaining a desired level of air pressure within the engine. One area in a gas turbine engine where bleed valves are used is in the various compressor stages. A bleed valve or series of valves may be used to control undesired effects such as engine surge. Also it is desirable to provide pressure control during certain dynamic engine conditions such as start up, acceleration, and deceleration. And, in general bleed valves are beneficial for engine control.
Bleed valves are subject to a variety of stresses and pressures in the engine environment. Debris and fouling present in the engine in particular may adversely impact the moveable parts on a bleed valve. Moveable parts that include carbon sealing rings, springs, pistons, and piston support shafts are thus subject to wear during normal engine operation. In order to increase the durability and reliability of bleed valves, it would be desirable to provide a bleed valve design that protects moveable parts from adverse conditions such as debris and fouling.
Certain bleed valve designs also have a pressurized state as their normal mode of operation. In this kind of design, for example, the bleed valve is closed when the engine is in a normal running state. However, to achieve the closed position, the bleed valve in that design must be pressurized through some supply of a pressurizing fluid. Thus this kind of design may be called the “Pressurized Closed” design. When the bleed valve is to be opened, the pressurizing fluid is relieved, and the valve is allowed to open. The weakness in the “Pressurized Closed” design is the fact that the valve must endure the effects of pressurizing during the majority of the time the engine is in operation. Pressurizing subjects valve components to stress, and can thus hasten valve breakdown. Seals and rings, for example, tend to lose effectiveness after experiencing prolonged periods of pressurization. Hence, it would be desirable to provide a bleed valve design that permits a bleed valve to be in the closed position during normal engine conditions but without the need to pressurize the valve to reach the closed position.
The harsh operating environment in the contemporary gas turbine engine also places increased stress on engine components such as bleed valves. In an attempt to increase the efficiencies and performance of contemporary gas turbine engines, engineers have progressively pushed the engine environment to more extreme operating conditions. The higher pressures that are now frequently specified specifically place increased demands on bleed valves. Thus in current jet engine design there is also a need for a bleed valve design that is robust and reliable.
Certain bleed valve designs are known; nevertheless, there is need for an improved design. Hence there is a need for a new bleed valve design that addresses one or more of the above-noted drawbacks. Namely, a bleed valve design is needed that will protect moveable parts from debris and fouling, and/or that permits the bleed valve to be in the closed/nonpressurized position during normal engine conditions, and/or that provides a robust and reliable design. The present invention addresses one or more of these needs.